1. Field of the Invention
This invention relates to single stroke linear pumps and is directed more particularly to a manifold assembly for mounting on the outlet of such a pump and operative to eliminate water hammer from operation of the pump.
2. Description of the Prior Art
In the U.S. Navy, it is customary to use a single stroke linear pump to eject small devices from submarines. In such pumps, air pressure operates on one side of a piston to drive the piston to accelerate a fluid, typically seawater, behind the small device, causing ejection of the device from the submarine. At the conclusion of the stroke, a dashpot cone projecting from the piston enters the pump water outlet. The outlet and the dashpot cone are configured so as to decelerate the piston near the end of its stroke. Upon completion of the stroke, the cone is disposed in, and operates to close, the pump water outlet.
A problem develops at the end of the stroke in that the water being ejected from the pump does not slow down appreciably as the piston slows. At the end of the stroke, the water being pushed by the piston separates from the piston, moving ahead while the piston slows and stops, creating a low pressure zone adjacent to the piston. Typically, the pressure in the zone is below atmospheric. The ejecting seawater reacts to the low pressure by reversing its direction of flow back towards the low pressure zone. The reverse flowing water meets the piston causing an instant of high water pressure in the aforesaid zone. The pressure spike in the zone adjacent to the piston causes the phenomenon commonly referred to as water hammer. Inasmuch as water hammer is accompanied by a significant noise, it is a particular problem in a submarine environment wherein radiated noise can reveal a presence and/or a position.
Accordingly, there is a need for means to eliminate water hammer in a single stroke linear pump. So that pumps currently in use will not have to be replaced, it is preferable that any such means be in the form of an add-on mechanism which can be attached to current pumps.